Adjustable voltage autotransformer



J n 1964 A. E. SNOWDON ETAL 3,136,967

ADJUSTABLE VOLTAGE AUTOTRANSFQRMER Original Filed July 7, 1959 m n m umiiiiiiiiili 9 Egg 48 25 57 6 68/- INVENTORS 7 5 Arlfiar E Snowdora L-a F/n'Z/nore .E k/bfmsorz 5:9 0 6.9 Elmer W Madser;

56 Eco/7e fl. Pays J? H 7 TOPNE Y5 United States Patent 3,136,967 ADJUSTABLE VOLTAGE AUTOTRANSFORMER Arthur E. Snowdon, Philmore E. Johnson, Elmer W.

Madsen, and George A. Page, Jr., Bristol, Conn, assignors to The Superior Electric Company, Bristol, Conn, a corporation of Connecticut Original application July 7, 1959, Ser. No. 825,485, now Patent No. 3,087,132, dated Apr. 23, 1963. Divided and this application Oct. 1, 1962, Ser. No. 227,395

Claims. (Cl. 336-149) The present invention relates to an electrical control device for providing an adjustable output voltage and more particularly to the type of device known as an autotransformer.

The present invention is a division of applicants copending application, Serial No. 825,485, filed July 7, 1959, now Patent No. 3,087,132, granted April 23, 1963 and entitled Adjustable Voltage Autotransfornier.

As commonly manufactured, an autotransformer of the type to which the instant invention is directed includes a coil composed of an annular core on which a length of wire is toroidally wound to form a Winding. A peripheral portion of each of the turns of the winding is formed into a commutating surface 011 which a brush is movable, being always in engagement with at least one turn. By moving the brush along the Winding, the output voltage may be adjusted.

An object of the present invention is to provide an autotransformer so constructed and arranged that it can safely control a larger amount of electrical current than in heretofore units of the same size.

A further object of the present invention is to provide an autotransformer of the above type which is rugged in construction and less subject to malfunctioning, is

composed of relatively few, economically produced parts that are capable of ready fabrication and assembly to form the complete autotransformen' A further object of the present invention is to provide a brush and brush holder unit which enables substitution of a brush simply and easily and which increases the durability and operation of the autotransformer by stabilizing the brush on the commutating surface on which it rides.

In achieving the above objects, the autotransformer of the present invention provides for an annular core having a toroidal winding and for mounting within the open center of the core a shaft which connects to the brush to move it on the commutating surface. According to the present invention, the shaft and brush arm are press fitted together to form a single assembly whereby the shaft In addiand brush relationship is maintained constant.

tion, the parts are arranged so that a substantial portion of the assembly is contained within the center of the core thereby enabling an axially longer core to be employed and hence an increase in the rating of the unit without increasing the overall thickness of the autotransformer.

A further feature of the present invention resides in the brush and brush holder of the brush arm which enables the brush to be readily removed when needed and a new brush substituted. This isaccomplished by constructing the brush and the brush arm to have cooperating portions and by tensioning the brush arm against the commutating surface to hold the brush in place and against the commutating surface. Moreover the brush and the brush holder stabilize the brush on the commu tating surface to maintain a flat area of the brush thereagainst by preventing movement of the brush relative to the holder in the path of movement of the holder While permitting relative pivotal movement therebetween in a plane perpendicular to the commutating surface to accommodate for unevenness in the commutating surface.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is a side view of the autotransformer of the present invention shown mounted on a panel, the latter being in section.

FIG. 2 is an end View looking in the direction of the arrows 2-2 of FIG. 1.

FIG. 3 is an elevation, somewhat enlarged and partly in section, of the details of the brush actuating mechanism of the autotransformer of the present invention.

FIG. 4 is an end View of the brush and brush holder forming part of the present invention.

FIG. 5 is a top View of the brush of the present invention.

FIG. 6 is a sectional view taken on the line 66 of FIG. 5.

FIG. 7 is a detail, looking at the side of the brush and brush holding portion of the brush arm.

Referring to the drawing, the autotransformer of the present invention is generally indicated by the reference numeral Ill-and has an annular coil including an annular core 11 preferably formed by spirally winding a length of paramagnetic material, such as iron. A pair of front and rear, annular end caps 12 and 13 abuts the ends of the core while a tubular member 14 encompasses the periphery of the core, these members being preferably formed of insulating plastic material. A winding 15, composed of a single length of electrical conducting wire,

is toroidally wound about the core over the members 12 and 13 in a single layer of juxtaposed turns. A commutating surface 16 is formed on the winding as by milling fiat a similar portion of each turn that is present on the raised annular portion 17 of the rear end cap 12.

Positioned against the front end cap 13, opposite the end cap having the commutating surface, is a circular base 18 having the cross-sectional shape shown and this base, for reasons hereinafter apparent, is formed of heat conductive, metallicmaterial such as cast aluminum. An electrically insulating disk 10, of mica for example, is secured to the back face of the base 18 to be positioned between it and the coil. A central aperture 20 is formed in the base and circumscribing the aperture is a larger circular indentation 21.

Positioned against the rear face of the coil is an annularend member 22 formed of insulating material such as plastic and having ashape Which-forms a hub .orcylindrical portion'23, an outwardly extending flange 24 and a central, stepped aperture 25 having portions of increasing diameter terminating at steps 26 and 27. A tubular sleeve 28 extends through the central apertures 20 and 25 and at one end portion has an outwardly extending flange 29 which abuts the step 26 formed in the annular member 22, while its other end portion is threaded as at 30. A nut 31 is threaded onto the portion 29 to fit within the indentation 21 and serves to unitarily clamp the base 18 and annular member 22 against the coil. To prevent rotation of the sleeve as the nut is screwed thereon the base 18 has a projection 32 fitting in a hole in the end cap 13 and the aperture 20 is keyed to the sleeve a by mating fiat portions (not shown).

The present invention provides for the clamping pressure of the base 18 and the member 22 to be parallel to a clamping pressure is exerted on the coil adjacent the 3 center edge portions thereof. To prevent radial movement of the base and member 22, the former has an annular hub 34 while the latter has the cylindrical portion 23, both of which extend into the center of the coil in closefitting engagement therewith.

A shaft 35 is rotatably mounted in the sleeve 28 and at one end portion is formed with a groove 36 in which is located a C-ring 37 that abuts against the end of the sleeve to prevent axial movement in one direction of the shaft. The other end of the shaft is formed with a reduced diameter portion 38 on which is press fitted an insulating bushing 39 formed of plastic material and having the shape shown which includes a shank 4t) and head An annular hub 42 having an inwardly extending flange 43 is press fitted onto the shank 40 of the bushing 39 to have the flange 43 abut against the head 41 of the bushing 39. A brush arm 44 preferably formed of electrical con ducting material that is also resilient, such as beryllium copper, has a collar portion 45 which circumscribes the head 41 and for maintaining the arm secured to the hub 42, both electrically and mechanically, the hub is provided with a peripheral skirt 46 that is spun over onto the collar portion 45 except for an opening 47 in the skirt through which the brush arm extends. The spunover skirt prevents axial movement of the arm while the sides of the opening prevent radial movement thereof relative to the hub. The other end of the brush arm 35 carries a brush 48 which will be hereinafter described that rides in electrical contact on the commutating surface 16. Also circumscribing the shank 40 of the bushing 39 is a saucer shaped annular spring washer 49 formed of resilient, conducting material and an end annular portion 50 of a conducting bar 51. The conducting bar 51 terminates in a terminal 52 and a screw 53 threads into an aperture in the rear end cap 12 to aid in securing the bar. The annular portion 50 of the conductor bar is within the stepped aperture 25 and passes through a radial cutout 54 in the flange 24.

With the above construction, it will be appreciated that current is conducted from the commutating surface of the Winding through the brush 48, the brush arm 44 the hub 42, the spring washer 49 to the annular portion 50 of the conducting bar 51 and then to the terminal 52, these parts being formed of electrical conducting material. In addition conduction of electricity to the shaft 35 is prevented by the parts 22 and 39 being formed of insulating material.

In the assembly of the autotransformer, the brush arm 44- is positioned on the hub 42 and made fast thereto by spinning over the skirt 46. The insulating bushing 39 is then press fitted into the hub 42 and the shaft is press fitted into the insulating bushing. The washer 49 and sleeve 28 are then positioned on the shaft and secured in place by the C-ring 37 to form a brush moving assembly. To complete the autotransformer of the present invention, the bar 51 and the member 22 are placed on the sleeve and the shaft and sleeve passed through the center of the coil to have positioned thereon the base 18 and the nut 31 which is threaded to clamp the parts together. The screw 53 is threaded into the rear end cap 12 to hold the conducting bar 51 against movement while the slot 54 formed in the flange also aids in restraining movement of the bar. With this structure, manufacturing tolerances can be absorbed because the spring washer 49 in addition to conducting current between the hub 42 and the bar 51 also serves to tension rearwardly the shaft by causing the bar 51 to abut the step 27 formed in the member 22 while pushing against the hub 42 thereby forcing the C-washer against the end of the sleeve.

The brush 48, as shown in FIGS. 4, and 6, includes an elongate carbon part 55 having one side beveled into a tip 56 having a flat rectangular surface which constitutes a flat carbon portion. The other sides 57 are rectilinear and flat and are secured in a rectangular cutout 53 formed in a block 59 of conducting material, as by soldering or brazing. The block 59 is of single-piece construction and includes a raised center section 60 of rectangular configuration which fits within a rectangular aperture 61 formed in the brush arm 44- with the sides of the aperture transverse to the length of the brush arm abutting the adjacent sides of the section 60 to prevent relative movement therebetween tangential to the commutating surface. The brush arm has an inwardly directed lip 62 on the backside of the aperture 61 and another inturned lip 63 formed on the front side. On either side of the aperture 61, the brush arm is formed to have oppositely disposed and aligned wing portions 64 and 65 each having a ridge 66 and 67 respectively with each ridge being arcuate in cross-section, as shown, and being approximately as long as the width of the aperture 61. The ridges engage flat rectangular surfaces 68 and 69 located below and at the sides of the raised section 60 and oppositely disposed on either side of the riding surface tip 56 with said surfaces 68 and 69 also constituting electrical conducting surfaces.

With the above construction of the brush and brush arm, it will be appreciated that the only pressure holding the brush in place is that exerted by the brush arm as it is tensioned by itself towards the commutating surface with the brush positioned therebetween, the brush arm in its at rest position not lying in a single plane since it is bent at the line 76 and if a brush were present, the brush arm would engage the outer periphery of the flange 24. If desired to remove the brush all that is required is the removal of the tension of the brush arm by bending it away from the commutating surface and letting the brush fall freely from the arm. A reversal of this procedure will enable the positioning of the brush in place. The brush arm is of substantial width and therefore has substantial resistance to twisting.

The tip 56 of the brush provides for a substantial fiat area of contact with the commutating surface Without engaging an undesirable number of turns and the present invention provides for maintaining the flat area of the brush completely in contact with the commutating surface, even though there may be irregularities in the flatness of the commutating surface. While theoretically it is desirable to have the commutating surface flat and in a single radial plane, it has been found that during manufacture the surface formed is not exactly flat but has portions that are flat yet at an angle to the radial plane. In order to compensate for variations, the brush and brush holder of the present invention prevents the brush from moving relative to the brush arm in the path that the brush arm moves and yet be permitted to move freely perpendicular to the path. This is accomplished by the ridges 66 and 67 each being of a length and extending substantially along the path of movement of the brush which prevents pivotal movement of the brush in the brush arm about the tip 56. However in order to compensate for the commutating surface not completely lying in a radial plane, the flat surfaces 68 and 69 of the brush are engaged only by the ridges 66 and 67 enabling it to be easily pivoted about the ridge for movement perpendicular to the brush path. Thus the brush and brush holder provide for prevention of movement along the commutating surface but yet provide for pivotal movement in a plane radial to the commutating surface thereby stabilizing the brush and maintaining substantial contact with the commutating surface by keeping the flat tip 56 completely in engagement thereto.

It will be understood from the above that electricity is conducted between the brush and brush arm only by the surfaces that mutually touch each other. These include the conducting surfaces 68 and 69 and the ridges 66 and 67 in addition to any other points or areas of contact between surfaces of the brush and brush arm which may oc cur at times but do not predictably occur at all times.

As shown in FIG. 1, the autotransformer 10 as illustrated is mounted on the back of a panel 71 having an aperture 72 through which part of the threaded portion 30 of the sleeve extends. A nut 73 threads on the portion to clamp the outer face of the circular base 18 against the inside surface of the panel. A knob 74 is mounted on the end of the shaft and in addition a dial 75 may be employed and preferably held in place by the nut 73. In order to facilitate connections to the device, there are provided three terminals 76 having the shape shown and secured to the peripheral covering 14 by staples 77 having bent over ends though, of course, other methods of securement maybe employed, if desired, Not shown are connections between two of the terminals and the ends of the winding, the other terminal being connected if desired to a tap intermediate the ends of the winding.

The conducting bar 51 is provided with a pair of outturned stops '78 which are engageable by the brush arm to prevent the brush from engaging the coil where there is no commutating surface.

It will accordingly be appreciated that there has been disclosed an autotransformer in which the shaft and brush arm assembly are composed of relatively few, easily manufactured parts that may be economically, if not automatically, assembled and which may then be easily assembled to the other parts of the autotransformer to fabricate it. The parts enable an increase of rating of the autotransformer unit without an increase in the thickness thereof by having substantial portions of the shaft and brush assembly recessed within the center in the core which enables a thicker core to be employed. The increased'rating produces more heat during use, however this heat is dissipated With a substantialrise in the autotransformer by its passing to the heat conducting circular base 16 which acts as a radiator and may dissiptate the heat by convection and/or conduction to the mounting panel.

Moreover the present invention facilitates interchangeability of the brush from the brush arm quickly and easily without disassembling any parts and yet provides for a brush that is stabilized and maintains a fiat area of contact with the commutating surface.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

We claim:

1. A brush for use with an adjustable autotransformer having a coil formed with a commutating surface comprising a carbon portion having a riding surface for riding on the commutating surface, a pair of conducting surfaces aligned, elevated above and oppositely disposed about the riding surface, each of the surfaces being fiat and rectangular with the length of the conducting surfaces being substantially identical and the width of the riding surface being less than the width of the conducting surfaces, said conducting surfaces being of substantially identical shape and being equally spaced from the center of the riding surface and being formed of metal, and a. raised section of rectangular configuration located between the conducting surfaces.

2. A commutating brush structure for use with an adjustable voltage autotransformer having a coil formed with a commutating surface and for conducting electric current with said coil comprising an elongate brush arm having substantially planar and aligned oppositely disposed wing portions, a brush including a flat carbon portion riding on the commutating surface in electrical engagement therewith and a pair of substantially planar conducting surfaces oppositely disposed about the portion, the conducting surfaces and the Wing portions being in engagement one to one to form two pairs of engaging surfaces, said pairs of engaging surfaces being formed to have contact with each other to enable the brush to be freely pivotable about an axis transverse to the brush arm by one surface of each of the pairs of engaging surfaces being formed to have a. projecting ridge extending transversely of the brush arm and the other surface being at least flat in the area of contact with the ridge, means for limiting pivotal movement of the brush comprising inbent lips formed on the brush arm engageable with ends of the brush, said engaging surfaces being of substantial transverse length to prevent pivotal movement of the brush about an axis parallel to said brush arm, a raised portions substantially abutting the adjacent sides of the raised section to prevent relative movement between the brush and brush arm transverse to the length of the brush arm, said brush and brush arm having mutually touching surfaces including their engaging surfaces and being electrically connected only by their mutually touching surfaces whereby electrical current is conducted from said brush to said brush arm solely through said touching surfaces.

3. A commutating brush structure for use with an adjustable voltage autotransformer having a coil formed with a commutating surface and for conducting electric current with said coil comprising an elongate brush arm having substantially planar and aligned oppositely disposed wing portions, a brush including a flat carbon portion riding on the commutating surface in electrical engagement therewith and a pair of substantially planar conducting surfaces oppositely disposed about the portion, the conducting surfaces and the wing portions being in engagement one to one to form two pairs of engaging surfaces, said pairs of engaging surfaces being formed to have contact with each other to enable the brush to be freely pivotable about an axis transverse to the brush arm by one surface of each of the pairs of engaging surfaces being formed to have a projecting ridge extending transversely of the brush arm and the other surface being at least flat in the area of contact with the ridge, said projecting ridges being arcuate in cross-section and being aligned, means for limiting pivotal movement of the brush comprising inbent lips formed on the brush arm engageable with ends of the brush, said engaging surfaces being of substantial transverse length to prevent pivotal movement of the brush about an axis parallel to said brush arm, a raised section formed on the brush between the conducting surfaces and an aperture formed in the brush arm between the wing portions, said raised section of the brush fitting within the aperture with the sides of the aperture at the Wing portions abutting the adjacent sides of the raised section to prevent relative movement between the brush and brush arm transverse to the length of the brush arm, said carbon portion of said brush engaging the commutating surface in alignment with the raised section between the pairs of engaging surfaces, said brush and brush arm having mutually touching surfaces including their engaging surfaces and being electrically connected only by their mutually touching surfaces whereby electrical current is conducted from said brush to said brush arm solely through said touching surfaces.

4. The invention as defined in claim 3 in which the brush arm is formed of resilient metal, the arcuate ridges are formed on the wing portions and the conducting surfaces of the brush are metal to render each of the pair of engaging surfaces a metal to metal contact.

5. A commutating brush structure for use with an adjustable voltage autotransformer having a coil formed with a commutating surface and for conducting electric current with the coil comprising an elongate brush arm formed of conducting metal and having at least one wing portion, a brush including a flat carbon portion riding on the commutating surface in electrical engagement therewith and at least one conducting surface formed of conducting metal, the conducting surface and the wing portion being in engagement to enable the brush to be freely pivotable about an axis transverse to the brush arm by one of the engaging surfaces being formed to have a projecting ridge extending transversely of the brush arm and the other surface being at least flat in' 7 8 the area of contact with the ridge, means for limiting touching surfaces whereby electrical current is conducted pivotal movement of the brush comprising inbent lips from said brush to said brush arm solely through said formed on the brush arm engageable with ends of the touching surfaces. brush, means for preventing pivotal movement of the brush about an axis parallel to said brush arm, and means 5 References Cited ill the file of this Patent for preventing relative movement between the brush and UNITED STATES PATENTS brush arm transverse to the length of the brush arm,

said brush and brush arm having mutually touching 1,271,793 Stanley July 9, 1918 surfaces including the metal to metal engaging surfaces 2,089,434 Schermerhorn Aug. 10, 1937 and being electrically connected only by their mutually 10 2,568,480 Barkis Sept. 18, 1951 

1. A BRUSH FOR USE WITH AN ADJUSTABLE AUTOTRANSFORMER HAVING A COIL FORMED WITH A COMMUTATING SURFACE COMPRISING A CARBON PORTION HAVING A RIDING SURFACE FOR RIDING ON THE COMMUTATING SURFACE, A PAIR OF CONDUCTING SURFACES ALIGNED, ELEVATED ABOVE AND OPPOSITELY DISPOSED ABOUT THE RIDING SURFACE, EACH OF THE SURFACES BEING FLAT AND RECTANGULAR WITH THE LENGTH OF THE CONDUCTING SURFACES BEING SUBSTANTIALLY IDENTICAL AND THE WIDTH OF THE RIDING SURFACE BEING LESS THAN THE WIDTH OF THE CONDUCTING SURFACES, SAID CONDUCTING SURFACES BEING OF SUBSTANTIALLY IDENTICAL SHAPE AND BEING EQUALLY SPACED FROM THE CENTER OF THE RIDING SURFACE AND BEING FORMED OF METAL, AND A RAISED SECTION OF RECTANGULAR CONFIGURATION LOCATED BETWEEN THE CONDUCTING SURFACES. 